FIG. 4 is a block diagram showing the construction of a known vehicular steering condition detecting apparatus. In FIG. 4, reference numeral 1 designates a steering wheel connected to a steering shaft 2 which is mounted on a front wheel steering mechanism 3.
The front wheel steering mechanism 3 is connected with a tie rod 4 to which a front wheel 5 is mounted.
A variable resistor 6 constituting a position sensor is connected to the steering shaft 2 so that the resistance thereof varies in accordance with the rotation of the steering shaft 2.
The variable resistor 6 is connected to an unillustrated power source so as to generate an output voltage which is proportional to the resistance thereof which varies with the rotation of the steering shaft 2. The output voltage of the variable resistor 6 is input to an analog/digital converter 7 (which is hereinafter referred to as an A/D converter).
The A/D converter 7 converts the output voltage of the variable resistor 6 into a digital value which is then output to a microcomputer 8.
The operation of the above apparatus will now be described. In accordance with the rotation of the steering wheel 1, the steering shaft 2 is thereby caused to rotate so that the resistance of the variable resistor 6 is accordingly varied. The variable resistor 6 generates an output voltage proportional to the varied resistance thereof to the A/D converter 7 where it is converted into a digital value.
The output of the A/D converter 7 is fed to the microcomputer 8 which calculates, based thereon, the absolute value of the steering angle and the angular velocity of the steering wheel 1, which are utilized as steering condition data for controlling various aspects of the operation of the vehicle.
With the known vehicular steering condition detecting apparatus as constructed above, a failure in the variable resistor 6 or a failure in the A/D converter 7 directly results in the destruction of the steering condition data prepared by the microcomputer 8. In addition, it is sometimes impossible to detect such a failure, thus providing the drawback that the control of the vehicle is seriously affected.
The present invention is intended to obviate the above-described drawback of the known vehicular steering condition detecting apparatus, and has for its object the provision of a vehicular steering condition detecting apparatus which is able to detect both a failure in the variable resistor for sensing the steering angle and a failure in the pulse generator for sensing the angular velocity of a steering wheel.